Here I was always thinking about the utility of heat zones the other way
around- like the reason I can't successfully grow many traditional
cottage garden perennials is because they's croak from too much heat!
Theresa

james singer wrote:

Finally found an instance when AHS heat zones were useful. Guy who
lives on Salt Spring Island, which is a few miles east of Victoria in
the gulf between Vancouver and Victoria. BC, and is in USDA hardiness
zone 9, wanted to know if he could grow avocados, which flourish in
zone 9 California and Florida. And the answer is no, because while
it's warm enough in winter, it isn't hot enough in summer. First time
it dawned on me--doh--that knowing one's heat zone might have some
utility in the real world.